Environmental monitoring

Report: Spatially balanced designs for surveying and monitoring the impact of mining on benthic biodiversity in NORI-D lease of the CCZ

• A spatially balanced sampling design improves the accuracy and efficiency of monitoring deep-sea mining impacts by ensuring even coverage across the NORI-D lease area.
• The design uses inclusion probabilities based on distance from mining zones to prioritise sampling near areas most affected by sediment plumes.
• The approach is flexible and scalable, allowing for different numbers of sampling voayges and deployments based on budget and logistical constraints.

This report outlines a scientifically robust method for designing surveys to monitor the environmental impacts of deep-sea mining in the NORI-D lease area of the Clarion–Clipperton Zone (CCZ). The focus is on using spatially balanced sampling to ensure that data collected are representative, statistically sound, and useful for assessing changes in benthic biodiversity.

The method applies Balanced Acceptance Sampling (BAS), which ensures that sampling points are evenly spread across the area of interest. This approach reduces redundancy and improves the ability to detect spatial patterns in species abundance and composition. The design also incorporates inclusion probabilities, which give higher sampling priority to areas closer to the mining paths—referred to as ‘the tracks’—where environmental impacts are expected to be greatest.

The report provides practical examples of how to implement this design under different scenarios, including low, medium, and high numbers of sampling deployments per monitoring voyage. It also shows how to adapt the design for ROV transects, using zigzag patterns to cover more ground efficiently. These designs are flexible and can be scaled up or down depending on available resources.

A key strength of the approach is that it allows for subsets of a master sample to be used while still maintaining spatial balance. This means that if fewer deployments or voyages are possible due to budget or time constraints, the integrity of the sampling design is preserved.

The report emphasises the importance of considering environmental gradients, such as sediment type, topography, and food availability, which influence species distribution. It also highlights the need to integrate different sampling methods (e.g., core sampling and ROV imaging) to capture a fuller picture of biodiversity.

Overall, this spatially balanced design provides a rigorous, adaptable, and cost-effective framework for monitoring the ecological impacts of deep-sea mining in a complex and data-poor environment.